test(cli): Verify precedence over external subcommands

crates/cargo-test-support/src/lib.rs

@@ -110,7 +110,9 @@ impl FileBuilder {
 
     fn mk(&mut self) {
         if self.executable {
-            self.path.set_extension(env::consts::EXE_EXTENSION);
+            let mut path = self.path.clone().into_os_string();
+            write!(path, "{}", env::consts::EXE_SUFFIX).unwrap();
+            self.path = path.into();
         }
 
         self.dirname().mkdir_p();

tests/testsuite/script.rs

@@ -9,6 +9,10 @@ fn main() {
 }
 "#;
 
+fn path() -> Vec<std::path::PathBuf> {
+    std::env::split_paths(&std::env::var_os("PATH").unwrap_or_default()).collect()
+}
+
 #[cargo_test]
 fn basic_rs() {
     let p = cargo_test_support::project()
@@ -68,6 +72,57 @@ error: no such command: `echo`
         .run();
 }
 
+#[cargo_test]
+#[cfg(unix)]
+fn manifest_precedence_over_plugins() {
+    let p = cargo_test_support::project()
+        .file("echo.rs", ECHO_SCRIPT)
+        .executable(std::path::Path::new("path-test").join("cargo-echo.rs"), "")
+        .build();
+
+    // With path - fmt is there with known description
+    let mut path = path();
+    path.push(p.root().join("path-test"));
+    let path = std::env::join_paths(path.iter()).unwrap();
+
+    p.cargo("-Zscript echo.rs")
+        .arg("--help") // An arg that, if processed by cargo, will cause problems
+        .env("PATH", &path)
+        .masquerade_as_nightly_cargo(&["script"])
+        .with_status(101)
+        .with_stdout("")
+        .with_stderr("\
+thread 'main' panicked at 'not yet implemented: support for running manifest-commands is not yet implemented', [..]
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+")
+        .run();
+}
+
+#[cargo_test]
+#[cfg(unix)]
+fn manifest_precedence_over_plugins_stable() {
+    let p = cargo_test_support::project()
+        .file("echo.rs", ECHO_SCRIPT)
+        .executable(std::path::Path::new("path-test").join("cargo-echo.rs"), "")
+        .build();
+
+    let mut path = path();
+    path.push(p.root().join("path-test"));
+    let path = std::env::join_paths(path.iter()).unwrap();
+
+    p.cargo("echo.rs")
+        .arg("--help") // An arg that, if processed by cargo, will cause problems
+        .env("PATH", &path)
+        .with_status(101)
+        .with_stdout("")
+        .with_stderr(
+            "\
+error: running `echo.rs` requires `-Zscript`
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn requires_nightly() {
     let p = cargo_test_support::project()